Abstract:
A new technique for producing an intense beam of polarized γ-rays is presented. This High-Intensity Gamma-ray Source (HIGS) will utilize the facilities of the new Duke Free Electron Laser Laboratory. This system includes the LINAC injector, the 1.3 GeV electron storage ring, and the OK-4 undulator. It will be shown that it is possible to tune the electron beam in a manner which allows the FEL photons to backscatter from an electron bunch, all within the ring. This leads to an intense beam of almost 100% linearly polarized γ-rays whose energy can be readily tuned from about 5 to greater than 200 MeV. Furthermore, beam energy spreads of less than 1% can be obtained by pure geometrical collimation. Details of the beam properties and background sources will be presented. It will be shown that this is an ideal beam for nuclear physics and nuclear astrophysics studies. One example of this which takes advantage of the flux, energy resolution and polarization of the beam, is the study of Δ33 excitations in finite nuclei. These intense polarized beams will also make it possible to perform precision measurements of the nucleon polarizabilities. And we will see that studies in the vicinity of the photo-pion production threshold can provide crucial tests of many of the recent predictions (Low Energy Theorems) of Chiral Perturbation Theory. Our final example will show how the very intense beams available at low energies can be used to determine astrophysically important capture cross sections by measurements of the inverse reactions.
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